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Typical Hem bend process capability

Typical Hem bend process capability

Typical Hem bend process capability

Hi Folks,

I'm looking into incorporating a hem bend into a sheet metal part and I'm trying to understand typical process capability that is expected when this form is created in manufacturing. Currently, our manufacturing facility doesn't have the tooling to perform the operation so we can't do any studies so i'm hoping this group could provide some insight.

I'm working with 2mm thick sheet metal and what we're really trying to understand is what the typical tolerance would be on the hem bend flange as it is bent 180deg onto itself.

Appreciate all and any feedback.


RE: Typical Hem bend process capability

The hem is really just like any other bend, it is made by first bending an acute angle (tighter than 90) and then hitting that same bend with flat tooling to complete the bend. Because of this tolerances will be similar to other bends. Typical values we use are +/- 0.015" bend to edge and +/- 0.020" bend to bend. These would apply only to coined hems, not ones with larger radii and a space in the hem flange. What kind of hem are you looking for?

RE: Typical Hem bend process capability

Thanks, hendersdc. We're looking at doing a coined hem bend or what I've heard described as a closed hem bend.

The insight you provided aligns with what we were looking at, which is encouraging. Thanks :)

RE: Typical Hem bend process capability

Are you hemming a panel to provide a cosmetic edge/edge protection, or are you actually bonding two panels together?

You may want to investigate robotic roller hemming if you are talking moderate or high volumes.

RE: Typical Hem bend process capability

Hint: If you look real close at a hem, even a coined one, you will see a teardrop or circular opening at its root, usually at least .005" diameter, so you can't really get a hem as thin as twice the material thickness. Sometimes that matters.

Mike Halloran
Pembroke Pines, FL, USA

RE: Typical Hem bend process capability

Great feedback, thanks everyone! This definitely helps :)

RE: Typical Hem bend process capability

Make sure when you do this, to select tooling that allows the hemmed edge to overlap the die by at least 2 times the thickness of the part, If you do not , you may notice strange discrepancies in the dimensioning of the hemmed part due to its not gripping the edge of the die as the angle forms.

You are judged not by what you know, but by what you can do.

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